Tents are available in many shapes, sizes, and levels of protection. Some models (especially domes) can be free-standing, requiring no stakes to hold them in shape. But they tend to be heavier, and trickier to set up. Unless you're sure you're never going to get rained on, a tent with a "rain fly" – a water resistant raincoat for your tent – is essential.
At the small end of the scale is the "bivy sack", which is little more than a raincoat for your sleeping bag; the most spacious ones are just big enough inside to carefully roll over.
A typical "1-person" tent might give you enough room inside to actually hunch over and maybe even scrunch up and turn around, but no more. A "2-person" tent is going to be big enough for just that: two people, lying right side-by-side. Depending on just how close you and your camping partner want to be, you might prefer a "2-to-3-person" tent (otherwise big enough for two adults and a child). If you're thinking of a larger tent so you can keep your gear with you (whether for easier access or to keep it out of the weather), a tent with a vestibule or an extended rain fly might be all you really need. By the time you get to a "4-person" tent, you're generally talking about something spacious enough that one or two people can sit upright in it, but heavy enough that you'll want to distribute the components among the people in your hiking party.
Although tents will keep most of the wind out, and usually trap air well enough to keep it warmer than outside, don't count on them to keep you ''warm''; that's your sleeping bag's job. The difference between a 3-season tent and a 4-season tent isn't their warmth, but the latter's ability to stand up to stronger winds and snow. Using a gas- powered lamp can also help to warm up your tent, but beware of setting fire to your tent and/ or melting something as the lantern casings get extremely hot.